OK, OK, I started this and I'm still having fun. Let's take a look at what
we have.
1) ALL TR's (TR2 -TR6) are transitional. That means that changes (some more
significant than others) occurred throughout each model. When the changes
became significant Triumph changed the TR model number by either adding a
letter or changing the number itself.
2) Frames - basically three types.
First - TR2/TR3/3A/3B frames - the same frame configuration with minor
changes.
Second - TR4 frame -- same frame design as the above except some outriggers
in the front to accommodate both the Michelotti body and some minor
suspension changes. (Name changed because the car looks completely different
and has other changeS of significance -- like a brand new body design and
rack and pinion steering.)
Third - TR4A frame -- completely different frame configuration (Called a
"bell and an "A" put together). Considered FAIRLY significant - Hence the
name change only from TR4 to TR4A. (Other changes were minor -- trim, minor
engine tweaks, etc.) This frame was necessarily designed to allow IRS in the
rear. This frame also continued through the TR6 -- WITH MINOR CHANGES. No
changes to the frame were major enough (even the engine mount positions to
accommodate the 6 cyl.) to qualify it as a different frame. (The reason for
the model name changes from TR4A to TR5/250 to TR6 were for the engine itself
and other significant body/suspension changes.)
3) One problem - The TR4A was also available in the US with the older TR4
"live axle." This was due to pressure from the US dealers. Triumph modified
the TR4A frame (the 'bell and the "A" ) to permit this "live axle" config.
That required new brackets to take the older type springs and no "bridge
piece" (The bridge piece was integral to the design of the TR4A frame since
the bridge piece was what allowed each rear wheel to be independently
suspended.) The "live axle" could not go on the car if the bridge piece was
there. (Two things can't occupy the same space at the same time.) So they
either 1) didn't weld the bridge piece onto the frame rails which means that
the frame itself, as designed, was MODIFIED or 2) (unlikely) they took the
bridge piece off after having put it on which also means that the frame was
MODIFIED. In either case the frame was not an "as designed" TR4A frame. If
you look at an IRS frame that bridge piece is integral and is a big sucker.
4) We could go on forever about changes to the frames BUT although Triumph
considered the TR4 to TR4A frame change to be significant (that's why they
added the A) they did not consider subsequent frame changes through the TR6
to be significant. These frame changes by themselves were considered minor
changes by the guys who were building the frames (hey - they didn't call the
TR4A the TR5 even though the whole frame design changed). Whether we
consider the frame changes from the TR4A through the TR6 as significant or
not is a moot point.
Anyone?? Cheers.
Art Kelly
In a message dated 23-Jun-99 13:02:22 Eastern Daylight Time,
dterrick@pangea.ca writes:
> Having pulled apart my 65 4A CTC 53***L (damn, no "O") for restoration, I
> can address this issue.
>
> There are many small diferences between a TR6 and TR4a frame, ost dealing
> with the area of the breast plate / driveshaft hoop area, and with the
> engine mounts (ask me about putting a TR6 frame on a 4).
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